1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and devices for preventing a leak of fluid through a threaded joint.
2. Discussion of the Background
In a compressor 1 illustrated in FIG. 1, which is a part, for example, of a natural gas processing installation, natural gas is compressed in a chamber 10. A stem 20 projects out of the chamber 10 through a flange 30. The stem 20 is locked to the flange 30 by a nut 40.
A joint having components assembled using complementary threads on their contact surfaces is usually designated as a threaded joint. The stem 20, the flange 30 and the nut 40, which have threads partially covering their outer or inner surfaces, form a threaded joint. The threads on the inner surfaces of the nut 40 and the flange 30 have shapes complementary to the threads on the outer surface of the stem 20. When threads have different and complementary shapes, they are sometimes called male/female threads.
Since a pressure inside the chamber 10 is higher than a pressure outside the chamber, the threaded joint is susceptible to gas leakage. For example, the pressure inside the chamber 10 may increase substantially when a reciprocating piston 60 moves towards the flange 30 thereby decreasing the volume of the chamber 10. A seal (not shown in FIG. 1) placed between the stem 20, the flange 30 and the nut 40 is used to prevent or limit the gas leaking outside the chamber 10.
Extracted natural gas may contain a large proportion of hydrogen sulfide (H2S). Although the hydrogen sulfide is a naturally occurring substance, inhaling air with a large percentage of hydrogen sulfide is poisonous. Therefore, when processing natural gas with a large proportion of hydrogen sulfide, ensuring a good sealing of the natural gas inside the processing installation becomes important for the safety of operators. If natural gas having a large proportion of hydrogen sulfide leaks outside the gas processing installation, the operators may be poisoned while in the vicinity of the installation.
A conventional threaded joint 100 is illustrated as an exploded view in FIG. 2. The threaded joint 100 includes a stem 120, a flange 130, a nut 140 and a seal 150, arranged along an axis 160, as shown in the figure.
A cross section of the threaded joint 100 as assembled is illustrated in FIG. 3. The stem 120 engages with the flange 130 and the nut 140. The seal 150 is mounted between the flange 130 and the nut 140.
The seal 150 of the threaded joint 100 is illustrated in FIG. 4 as viewed in a plane perpendicular on the axis 160. The seal 150 includes an outer portion 152, which is a flat metal washer, and a rubber portion 154 attached to an internal rim of the outer portion 152. The rubber portion 154 includes a rubber ring 156 and three rubber flaps 158. Each of the rubber flaps 158 covers a respective area between a chord and a corresponding arch. The arches are equal and equally spaced on a circumference of the rubber ring 156.
FIG. 5 is an enlarged view of a portion of FIG. 3. When the stem 120, the flange 130, the nut 140 and the seal 150 are assembled, the outer portion 152 (as marked in FIG. 4) of the seal 150 is positioned between the flange 130 and the nut 140. In this configuration, the torque that can be applied to the nut 140 is relatively low.
The rubber flaps 158 are intended to cover the stem 120, inside the flange 130, in a portion in which the flange may have no threads. When the stem 120 advances from right to left along the axis 160, in FIG. 3, the rubber flaps tend to move in the same direction and may become shredded.
It has been observed that after a few movements of the stem 120 along the axis 160, the rubber portion 154 of the seal 150 becomes shredded, and the shredding substantially lowers the capability of the seal 150 to prevent the gas leaking. Therefore, the seal 150 has to be replaced often. The replacement of the seal requires at least a partial disassembly of the compressor, and, therefore, it adds to the downtime of the gas processing installation.
Even if the seal 150 operates at design parameters, in absence of a tight fit ensured when a substantial torque can be applied to the nut 140, the efficiency of the sealing is too low for being safely used when the natural gas has a large proportion of hydrogen sulfide.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.